Experimental investigation on anchor drop and drag

• Main Author: Xie, Clement Keqin
• Other Authors: Low Ying Min
• Format: Final Year Project
• Language: English
• Published: 2009
• Subjects: DRNTU::Engineering::Civil engineering::Water resources
• Online Access: http://hdl.handle.net/10356/16044
• Institution: Nanyang Technological University

Marine and offshore industry has been growing significantly over the past few years. However due to the stellar growth in these industries, the risk of hazards pertaining to offshore pipelines damage by ship anchors inevitably rises. The significant damage to the pipeline may lead to severe environmental effect and risk to safety. It is therefore a major concern for marine engineers in the design of buried pipelines. The main objective of this report is to understand the impact velocity and the penetration depth of different dropped anchors and eventually recommend the burial depth of the offshore pipeline. Literature reviews relevant to the research were studied. In this research, direct free fall tests on different anchor shapes were conducted to investigate their effect on the impact velocity and the penetration depth on coarse and fine sand. Plumb blob, metal rod and admiralty design pattern anchor were chosen to represent the different anchor shapes. The objects were dropped in a tank at a designated height of 90cm above the sand surface. The motion of the anchor drop were captured and studied with a Photron Hi-Speed Camera. Experiment findings showed that plumb blob has the largest impact velocity and penetration depth in coarse and fine sand as compare to anchor and rod. Plumb blob has an aerodynamic shape that experience smaller frictional resistance along anchor-soil interface during penetration. Its high mass and impact velocity generates a greater kinetic energy and penetrating force to achieve a significant penetration depth. It was also discovered that the penetration depths in fine sand were significantly smaller than in coarse sand for all the anchor shapes. This is due to the dense interlocking between fine sand particles during consolidation in water resulting in higher soil penetration resistance. From the experimental analysis, it was observed that there is an approximate linear increase in embedment depth with impact velocity. Other area of studies also found out that an increase in anchor drop height will caused an increase in impact velocity and penetration depth. Based on the research, anchor shape, mass and dimensions are important criteria that should be taken into consideration when designing the required burial depth of offshore pipeline.